We　investigate　the　aging　behavior　of　High-Density　Polyethylene　(HDPE)　pipelines,　specifically　comparing　the　Pipe　Body　(PB)　and　Butt-Fusion　Welded　Joint　(BFWJ)　under　thermal　oxidative　and　hydrothermal　accelerated　aging　conditions.　Our　results　indicate　that　the　performance　disparity　between　PB　and　BFWJ　diminishes　as　aging　time　increases.　We　also　find　that　the　specimen　type　affects　the　quantity　of　polyethylene　fibers,　with　hydrothermal　aging　significantly　affecting　the　cohesive　force　among　these　fibers　in　both　PB　and　BFWJ.　These　findings　on　differential　aging　processes　of　PB　and　BFWJ　contribute　to　a　deeper　understanding　of　HDPE　pipeline　durability　and　offer　practical　recommendations　for　mitigating　degradation　risks　associated　with　these　disparities.　This　research　underscores　the　importance　of　considering　specific　aging　behaviors　in　the　maintenance　and　reliability　assessment　of　HDPE　pipeline　systems　used　in　energy　transport,　industrial,　and　agricultural　applications.　©　The　Author(s),　under　exclusive　licence　to　Springer　Nature　B.V.　2024.